The UIApplication class provides a centralized point of control and coordination for applications running on iOS.
Every application must have exactly one instance of UIApplication (or a subclass of UIApplication). When an application is launched, the UIApplicationMain function is called; among its other tasks, this function creates a singleton UIApplication object. Thereafter you can access this object by invoking the sharedApplication class method.
This object has a method setStatusBarHidden, which can be used to change the visibility of the status bar.
To hide the status bar, use:
[[UIApplication sharedApplication] setStatusBarHidden:YES withAnimation:UIStatusBarAnimationFade];
To show the status bar, use:
[[UIApplication sharedApplication] setStatusBarHidden:NO withAnimation:UIStatusBarAnimationFade];